Surface-modified, pyrogenically prepared silicas

ABSTRACT

Surface-modified, pyrogenically prepared silica is prepared by subjecting the pyrogenically prepared silica, which is in the form of aggregates of primary particles and possesses a BET surface area of 150±15 m 2 /g, the aggregates having an average area of 12 000-20 000 nm 2 , an average equivalent circle diameter (ECD) of 90-120 nm and an average circumference of 1150-1700 nm, to surface-modification in a known way. It can be used as a filler for thickening liquid systems.

The invention relates to surface-modified, pyrogenically prepared silicas, to a process for preparing them and to their use.

The preparation of surface-modified pyrogenic (fumed) silicas from pyrogenically prepared silicas by surface modification is known. Silicas prepared in this way find use in many fields of application: for example, for controlling the rheology of liquid systems, in resins, and for use in adhesives. In these applications, great importance attaches not only to the thickening effect but also to the ease of incorporation into the liquid system.

The known surface-modified, pyrogenic silicas have the disadvantage that their ease of incorporation into liquid systems is unsatisfactory.

The object was therefore to prepare surface-modified pyrogenic silicas which possess an improved ease of incorporation into liquid systems without detriment to other important properties, such as the thickening effect.

The invention provides surface-modified, pyrogenically prepared silicas which are characterized in that their ease of incorporation into liquid systems is improved without detriment to the thickening effect.

The invention further provides a process for preparing the surface-modified, pyrogenically prepared silica, which is characterized in that the pyrogenically prepared silica, which is in the form of aggregates of primary particles and possesses a BET surface area of 150±15 m²/g, the aggregates having an average area of 12 000-20 000 nm², an average equivalent circle diameter (ECD) of 90-120 nm and an average circumference of 1150-1700 nm, is surface-modified in a known way.

The pyrogenically prepared silica used as starting material is known from EP 1 681 266 A2.

The surface modification can be accomplished by spraying the silicas where appropriate with water and subsequently with the surface modifier. Spraying may also take place in the opposite order. The water used may have been acidified with an acid, hydrochloric acid, for example, to a pH of 7 to 1. If two or more surface modifiers are employed, they can be applied together, or separately, in succession or as a mixture.

The surface modifier or modifiers may have been dissolved in suitable solvents. The end of spraying may be followed by mixing for 5 to 30 minutes more.

The mixture is subsequently treated thermally at a temperature of 20 to 400° C. over a period of 0.1 to 6 h. The thermal treatment may take place under inert gas, such as nitrogen, for example.

An alternative method of surface modification of the silicas can be accomplished by treating the silicas with the surface modifier in vapour form and then thermally treating the mixture at a temperature of 50 to 800° C. over a period of 0.1 to 6 h. The thermal treatment may take place under inert gas, such as nitrogen, for example.

The temperature treatment may also take place over a number of stages at different temperatures.

The surface modifier or modifiers can be applied using single-fluid, two-fluid or ultrasound nozzles.

The surface modification can be carried out in heatable mixers and dryers with spraying installations, continuously or batchwise. Suitable apparatus may for example be the following: ploughshare mixers, plate dryers, fluidized-bed dryers or fluid-bed dryers.

As surface modifier it is possible to use at least one compound from the group of the following compounds:

-   a) organosilanes of type (RO)₃Si(C_(n)H_(2n+1)) and     (RO)₃Si(C_(n)H_(2n−1))     -   R=alkyl, such as for example, methyl-, ethyl-, n-propyl-,         isopropyl-, butyl-     -   n=1-20 -   b) organosilanes of type R′_(x)(RO)_(y)Si(C_(n)H_(2n+1)) and     R′_(x)(RO)_(y)Si(C_(n)H_(2n−1))     -   R=alkyl, such as for example, methyl-, ethyl-, n-propyl-,         isopropyl-, butyl-     -   R′=alkyl, such as for example, methyl-, ethyl-, n-propyl-,         isopropyl-, butyl-     -   R′=cycloalkyl     -   n=1-20     -   x+y=3     -   x=1, 2     -   y=1, 2 -   c) haloorganosilanes of type X₃Si(C_(n)H_(2n+1)) and     X₃Si(C_(n)H_(2n−1))     -   X=Cl, Br     -   n=1-20 -   d) haloorganosilanes of type X₂(R′)Si(C_(n)H_(2n+1)) and     X₂(R′)Si(C_(n)H_(2n−1))     -   X=Cl, Br     -   R′=alkyl, such as for example, methyl-, ethyl-, n-propyl-,         isopropyl-, butyl-     -   R′=cycloalkyl     -   n=1-20 -   e) haloorganosilanes of type X(R′)₂Si(C_(n)H_(2n+1)) and     X(R′)₂Si(C_(n)H_(2n−1))     -   X=Cl, Br     -   R′=alkyl, such as for example, methyl-, ethyl-, n-propyl-,         isopropyl-, butyl-     -   R′=cycloalkyl     -   n=1-20 -   f) organosilanes of type (RO)₃Si(CH₂)_(m)—R′     -   R=alkyl, such as methyl-, ethyl-, propyl-     -   m=0.1-20     -   R′ methyl-, aryl (for example —C₆H₅, substituted phenyl         radicals)         -   —C₄F₉, —OCF₂—CHF—CF₃, —C₆F₁₃, —O—CF₂—CHF₂         -   —NH₂, —N₃, —SCN, —CH═CH₂, —NH—CH₂—CH₂—NH₂,         -   —N—(CH₂—CH₂—NH₂)₂         -   —OOC(CH₃)C═CH₂         -   —OCH₂—CH(O)CH₂         -   —NH—CO—N—CO—(CH₂)₅         -   —NH—COO—CH₃, —NH—COO—CH₂—CH₃, —NH—(CH₂)₃Si (OR)₃         -   —S_(x)—(CH₂)₃Si(OR)₃         -   —SH         -   —NR′R″R′″(R′=alkyl, aryl; R′═H, alkyl, aryl; R′″═H, alkyl,             aryl, benzyl, C₂H₄NR″″R′″″ with R″″═H, alkyl and R′″″═H,             alkyl) -   g) organosilanes of type (R″)_(x)(RO)_(y)Si(CH₂)_(m)—R′

$\begin{matrix} {R^{''} = {alkyl}} \\ {= {cycloalkyl}} \end{matrix}$ $\begin{matrix} {{x + y} = 3} \\ {{x = 1},2} \\ {{y = 1},2} \\ {m = {0.1\mspace{14mu} {to}\mspace{14mu} 20}} \end{matrix}$

-   -   R′=methyl-, aryl (for example —C₆H₅, substituted phenyl         radicals)         -   —C₄F₉, —OCF₂—CHF—CF₃, —C₆F₁₃, —O—CF₂—CHF₂         -   —NH₂, —N₃, —SCN, —CH═CH₂, —NH—CH₂—CH₂—NH₂,         -   —N—(CH₂—CH₂—NH₂)₂         -   —OOC(CH₃)C═CH₂         -   —OCH₂—CH(O)CH₂         -   —NH—CO—N—CO—(CH₂)₅         -   —NH—COO—CH₃, —NH—COO—CH₂—CH₃, —NH—(CH₂)₃Si (OR)₃         -   —S_(x)—(CH₂)₃Si (OR)₃         -   —SH         -   —NR′R″R′″(R′=alkyl, aryl; R″═H, alkyl, aryl; R′″═H, alkyl,             aryl, benzyl, C₂H₄NR″″R′″″ with R″″═H, alkyl and R′″″═H,             alkyl)

-   h) haloorganosilanes of type X₃Si(CH₂)_(m)—R′     -   X=Cl, Br     -   m=0.1-20     -   R′=methyl-, aryl (for example —C₆H₅, substituted phenyl         radicals)         -   —C₄F₉, —OCF₂—CHF—CF₃, —C₆F₁₃, —O—CF₂—CHF₂         -   —NH₂, —N₃, —SCN, —CH═CH₂,         -   —NH—CH₂—CH₂—NH₂         -   —N—(CH₂—CH₂—NH₂)₂         -   —OOC(CH₃)C═CH₂         -   —OCH₂—CH(O)CH₂         -   —NH—CO—N—CO— (CH₂)₅         -   —NH—COO—CH₃, —NH—COO—CH₂—CH₃, —NH—(CH₂)₃Si (OR)₃         -   —S_(x)—(CH₂)₃Si (OR)₃         -   —SH

-   i) haloorganosilanes of type (R)X₂Si(CH₂)_(m)—R′     -   X=Cl, Br     -   R=alkyl, such as methyl-, ethyl-, propyl-     -   m=0.1-20     -   R=methyl-, aryl (e.g. —C₆H₅, substituted phenyl radicals)         -   —C₄F₉, —OCF₂—CHF—CF₃, —C₆F₁₃, —O—CF₂—CHF₂         -   —NH₂, —N₃, —SCN, —CH═CH₂, —NH—CH₂—CH₂—NH₂,         -   —N—(CH₂—CH₂—NH₂)₂         -   —OOC(CH₃)C═CH₂         -   —OCH₂—CH(O)CH₂         -   —NH—CO—N—CO—(CH₂)₅—NH—COO—CH₃, —NH—COO—CH₂—CH₃,             —NH—(CH₂)₃Si(OR)₃, it being possible for R to be methyl-,             ethyl-, propyl-, butyl-         -   —S_(x)—(CH₂)₃Si(OR)₃, it being possible for R to be methyl-,             ethyl-, propyl-, butyl-         -   —SH

-   J) haloorganosilanes of type (R)₂XSi(CH₂)_(m)—R′     -   X=Cl, Br     -   R=alkyl     -   m=0.1-20     -   R′=methyl-, aryl (e.g. —C₆H₅, substituted phenyl radicals)         -   —C₄F₉, —OCF₂—CHF—CF₃, —C₆F₁₃, —O—CF₂—CHF₂         -   —NH₂, —N₃, —SCN, —CH═CH₂, —NH—CH₂—CH₂—NH₂,         -   —N—(CH₂—CH₂—NH₂)₂         -   —OOC(CH₃)C═CH₂         -   —OCH₂—CH(O)CH₂         -   —NH—CO—N—CO— (CH₂)₅         -   —NH—COO—CH₃, —NH—COO—CH₂—CH₃, —NH—(CH₂)₃Si (OR)₃         -   —S_(x)—(CH₂)₃Si (OR)₃         -   —SH

-   k) silazanes of type

-   -   R=alkyl, vinyl, aryl     -   R′=alkyl, vinyl, aryl

-   l) cyclic polysiloxanes of type D 3, D 4, D 5, with D 3, D 4 and D 5     meaning cyclic polysiloxanes having 3, 4 or 5 units of type     —O—Si(CH₃)₂—.     -   e.g. octamethylcyclotetrasiloxane=D 4

-   m) polysiloxanes or silicone oils of type

-   R=alkyl such as C_(n)H_(2n+1), n being 1 to 20, aryl, such as phenyl     radicals and substituted phenyl radicals, (CH₂)_(n)—NH₂, H -   R′=alkyl such as C_(n)H_(2n+1), n being 1 to 20, aryl, such as     phenyl radicals and substituted phenyl radicals, (CH₂)_(n)—NH₂, H -   R″=alkyl such as C_(n)H_(2n+1), n being 1 to 20, aryl, such as     phenyl radicals and substituted phenyl radicals, (CH₂)_(n)—NH₂, H -   R′″=alkyl such as C_(n)H_(2n+1), n being 1 to 20, aryl, such as     phenyl radicals and substituted phenyl radicals, (CH₂)_(n)—NH₂, H

As surface modifiers it is preferred to use the following silanes:

octyltrimethoxysilane, octyltriethoxysilane, hexamethyldisilazane, 3-methacryloyloxypropyltrimethoxysilane, 3-methacryloyloxypropyltriethoxysilane, hexadecyltrimethoxysilane, hexadecyltriethoxysilane, dimethylpolysiloxane, glycidyloxypropyltrimethoxysilane, glycidyloxypropyltriethoxysilane, nonafluorohexyltrimethoxysilane, tridecafluorooctyltrimethoxysilane, tridecafluorooctyltriethoxysilane, aminopropyltriethoxysilane, hexamethyldisilazane and polydimethylsiloxane.

With particular preference it is possible to use hexamethyldisilazane, dimethylpolysiloxane, octyltrimethoxysilane, octyltriethoxysilane and polydimethylsiloxane

More particularly it is possible to use polydimethylsiloxane.

The surface-modified, pyrogenically prepared silica of the invention can be used as a filler for resins.

The invention further provides resins which comprise the surface-modified, pyrogenically prepared silica of the invention.

The invention features the following advantages: greater ease of incorporation into liquid systems without detriment to the thickening effect.

EXAMPLES Preparation of the Comparative Silica

2 kg of silica 11 (Table 4 from EP 1681266) were charged to a mixer and, with mixing, were sprayed with 0.42 kg of Rhodorsil oil 47 V 100 (polydimethylsiloxane) by means of a two-fluid nozzle. After the end of spraying, mixing was continued for 15 minutes and the reaction mixture was subsequently heated under a nitrogen atmosphere.

Preparation of the Inventive Silicas Example

2 kg of silica 1 (Table 4 from EP 1 681266) were charged to a mixer and, with mixing, were sprayed with 0.42 kg of Rhodorsil oil 47 V 100 (polydimethylsiloxane) by means of a two-fluid nozzle. After the end of spraying, mixing was continued for 15 minutes, and the reaction mixture was subsequently heated under a nitrogen atmosphere.

Physicochemical Data

BET specific Tapped Loss on Loss on C surface density drying ignition content area Designation [g/l] [%] [%] pH [%] [m²/g] Comparative 67 0.1 4.4 5.8 4.6 95 silica Inventive 65 0.1 4.4 5.7 4.6 94 silica

Determination of Incorporation Characteristics

The incorporation characteristics were determined by measuring the time required for the silica to be homogenized in a resin.

This is done by weighing out 100 g of Palatal A 410 into a 350 ml beaker and heating it at 25° C. in a water bath.

The beaker is introduced into the aluminium insert of the mounting device of the dissolver (Getzmann Dispermat).

The stirrer (disc diameter 30 mm) is immersed to its target depth of t=10 mm above the base of the beaker, and switched on at a speed n of 500 min⁻¹.

3 g of silica are placed uniformly onto the surface of the resin, and the stopwatch is started.

A measurement is made of the time required for the silica to be homogenized.

The elapsed time is translated into a school-grade system (grade 1-grade 5). Grade 1 corresponds to very good (rapid) incorporation. Grade 5 corresponds to very poor (slow) incorporation.

Determination of Thickening Effect in an Epoxy Resin

201.92 g (92.15%) of Renalm M1 and 8.08 g (3.85%) of silica are weighed out into a 350 ml PE beaker.

The dissolver disc (disc diameter: d=50 mm) is immersed to the middle point of the beaker and the sample is homogenized at 1000 rpm.

In this case the beaker is sealed with the perforated lid in order to prevent the silica escaping as dust.

As soon as the silica has been fully incorporated, the disc is immersed to a depth of 10 mm above the base of the beaker. Dispersion is carried out for 3 minutes at a speed of 3000 rpm. During this time, air is removed under vacuum.

The dispersed sample is transferred to a 250 ml glass bottle.

The sample is stored in a water bath at 25° C. for 90 minutes.

After 90 minutes the sample is agitated with a spatula for 1 minute. Subsequently the viscosity of the sample is determined using a Brookfield DV III.

For this purpose the spindle of the Brookfield rheometer is immersed to the defined mark. Measurement is carried out as follows:

5 rpm—value read off after 60 seconds

50 rpm—value read off after 30 seconds.

The values read off are the viscosities [Pa*s] at the respective rpm.

Incorporation Characteristics and Thickening Effect—Results

Thickening Thickening Incorporation at 5 rpm at 50 rpm Designation (grade) [Pa*s] [Pa*s] Comparative 4 70 000 15 760 silica Inventive silica 1 70 600 15 360

It is clearly apparent that the inventive silica exhibits much better incorporation characteristics. This means that it is incorporated more rapidly than the comparative silica, despite the fact that not only the thickening effect but also the other physico-chemical data are comparable. 

1. Surface-modified, pyrogenically prepared silica characterized in that it possesses improved ease of incorporation into liquid systems.
 2. Process for preparing the surface-modified, pyrogenically prepared silica according to claim 1, characterized in that the pyrogenically prepared silica, which is in the form of aggregates of primary particles and possesses a BET surface area of 150±15 m²/g, the aggregates having an average area of 12 000-20 000 nm², an average equivalent circle diameter (ECD) of 90-120 nm and an average circumference of 1150-1700 nm, is surface-modified in a known way.
 3. Process according to claim 2, characterized in that dimethylpolysiloxanes are utilized as surface modifier.
 4. Process according to claim 2, characterized in that the silicas are sprayed if appropriate with water and subsequently with the surface modifier.
 5. Process according to claim 2, characterized in that the silicas are treated with the surface modifier in vapour form and the mixture is subsequently treated thermally at a temperature of 50 to 800° C. over a period of 0.1 to 6 h.
 6. Use of the surface-modified, pyrogenically prepared silica for thickening liquid systems.
 7. Use of the surface-modified, pyrogenically prepared silica for thickening resins. 